There are three common ways to use the word 'as'
1. Conjunction- To join two clauses
a. To join two
clauses when two things are happening at the same time.
for example
I was singing as I was
waiting for the train.
b . To state the reason for an action ( it can be used like
'because or since')
I was late as I slept
in.
2. Comparative adverb
for example
He was as hairy as a dog.
(He was like a dog he was so hairy.)
3. Preposition
To show the function of something or someone
He used the pen as a
knife
(He used the pen like a knife)
